Electrically erasable programmable read only memory (EEPROM) structures are commonly used in integrated circuits for nonvolatile data storage. One EEPROM device uses a silicon-oxide-nitride-oxide-silicon (SONOS) structure, in which charge is stored in the nitride layer. An advantage of the SONOS structure is the ease of processing due to its simpler layer structure.
However, it may be difficult to discharge (erase) the nitride layer of the SONOS structure. If the oxide between the silicon and nitride (i.e., bottom oxide) is too thin, direct tunneling of electrons will occur during read of the device. This tunneling is undesirable because it causes disturb problems. But if the bottom oxide is made thick enough to prevent tunneling, it is difficult to erase because holes are prevented from tunneling. While hot hole erase could be used, this process damages the bottom oxide and can lead to degraded reliability. Thus, a need exists for a process that can be used to erase SONOS devices without a concern of degraded reliability.
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